Hydraulic excavator drive system

Abstract

A hydraulic excavator drive system includes: first and second pumps; arm cylinder; arm first control valve connected to the cylinder by an arm crowding supply line and arm pushing supply line; arm second control valve connected to the supply lines by a first and second replenishment line; and arm operation device that outputs an operation signal corresponding to an inclination angle of an operating lever. The arm second control valve is configured so, when performing an arm crowding operation, an opening area at a meter-in side changes in accordance with the operation signal, and an opening area at a meter-out side is: kept to zero when a predetermined condition is not satisfied; and kept to zero until the operation signal becomes a setting value or greater, and when the operation signal has become the setting value or greater, increases to a maximum value when the predetermined condition is satisfied.

The invention claimed is: 
     
       1. A hydraulic excavator drive system comprising:
 a first pump; 
 a second pump; 
 an arm cylinder; 
 an arm first control valve connected to the first pump and a tank, and connected to the arm cylinder by an arm crowding supply line and an arm pushing supply line; 
 an arm second control valve connected to the second pump and the tank, connected to the arm crowding supply line by a first replenishment line, and connected to the arm pushing supply line by a second replenishment line; and 
 an arm operation device including an operating lever that receives an arm crowding operation and an arm pushing operation, the arm operation device outputting an operation signal corresponding to an inclination angle of the operating lever, wherein 
 the arm second control valve is configured such that, at a time of performing the arm crowding operation,
 an opening area at a meter-in side, which is the first replenishment line side, of the arm second control valve changes in accordance with the operation signal, and 
 an opening area at a meter-out side, which is the second replenishment line side, of the arm second control valve is:
 kept to zero in a case where a predetermined condition is not satisfied; and 
 kept to zero when the operation signal is a setting value or less, and when the operation signal is mater than the setting value, increases to a maximum value in a case where the predetermined condition is satisfied. 
 
 
 
     
     
       2. The hydraulic excavator drive system according to  claim 1 , wherein
 the arm second control valve includes a first pilot port for the arm crowding operation and a second pilot port for the arm pushing operation, 
 the hydraulic excavator drive system further comprises:
 a solenoid proportional valve connected to the first pilot port; and 
 a controller that feeds, to the solenoid proportional valve, a command current corresponding to the operation signal outputted from the arm operation device, and 
 
 in the case where the predetermined condition is not satisfied, the controller limits the command current to a constant value when the operation signal has become the setting value or greater, and in the case where the predetermined condition is satisfied, the controller refrains from limiting the command current regardless of whether or not the operation signal has become the setting value or greater. 
 
     
     
       3. The hydraulic excavator drive system according to  claim 1 , wherein
 the predetermined condition is a condition that a pressure of the arm crowding supply line is higher than a threshold. 
 
     
     
       4. The hydraulic excavator drive system according to  claim 1 , further comprising an engine that drives the first pump and the second pump, wherein
 the predetermined condition is a condition that a rotational speed of the engine is higher than a threshold. 
 
     
     
       5. The hydraulic excavator drive system according to  claim 1 , wherein
 the predetermined condition is a condition that at least one of a discharge pressure of the first pump and a discharge pressure of the second pump is higher than a threshold. 
 
     
     
       6. The hydraulic excavator drive system according to  claim 2 , wherein
 the predetermined condition is a condition that a pressure of the arm crowding supply line is higher than a threshold. 
 
     
     
       7. The hydraulic excavator drive system according to  claim 2 , further comprising an engine that drives the first pump and the second pump, wherein
 the predetermined condition is a condition that a rotational speed of the engine is higher than a threshold. 
 
     
     
       8. The hydraulic excavator drive system according to  claim 2 , wherein
 the predetermined condition is a condition that at least one of a discharge pressure of the first pump and a discharge pressure of the second pump is higher than a threshold.